Hello, SFIA audio listeners. In this month's Nebula exclusive, big alien theory,

we're asked at the reason alien civilizations might be rare is because most aliens are huge.

To hear it and every episode early and add-free, plus hours of bonus content,

check out go.nebola.tv slash Isaac Arthur and use my code, Isaac Arthur.

One of Earth's most unique features is the enormous gemstone in our sky we call the moon,

but could the moon be the reason why we even exist?

Ever since we first began realizing how ancient and immense the universe is, we've been asking

the question of if we are alone, and if not, where is everybody?

Or where did everyone go?

All those stars, many like our own, surely had planets too, and our better telescopes

of modern times confirm that planets are quite common. Still, those

telescopes are not strong enough yet to reveal Earth-like planets. They can only see those

planets that are either immense in scale, like Jupiter, or very close to their sun. Virtually every

exoplanet we have found is both big and hot. Even the so-called Earth-like

planets often overhyped in science journalism rarely approximately Earth any better than Venus

does for temperature or Neptune does for size. Nonetheless, we tend to assume planets in our size

and temperature range are common enough, and we also tend to assume planets in our size and temperature range are common enough,

and we also tend to assume moons around all those planets are common enough, too.

Lots of planets have them that we can see.

Indeed, Jupiter and Saturn both have many moons and larger ones, too, of a size with our own.

Only Venus and Mercury are without known moons, so close to our sun that its gravity would

tend to make capturing a satellite harder.

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